Make `runTheSPEACWeightings` more efficient

Some of the tension computations were repeated independently by the tension
functions. These intermediary results are now precomputed in
`runTheSPEACWeightings`.
Add small benchmark, update .gitignore
Better docs for `fixTriplets`, small aesthetic improvements
Update 'metricTension' to use 'Data.Array'
Make "computeDurationTensions'" pointfree